ISC, ISCe, QSC8.3, ISL, ISLe3, ISLe4 and QSL9 Engines – Intake Manifold Pressure (Boost) is Below Normal

Symptom Tree  t097

This is symptom tree t097
Cause Correction

Electronic fault codes active or high counts of inactive fault codes

Read the fault codes with an electronic service tool. Refer to Section TF in Troubleshooting and Repair Manual, ISB, QSB4.5, QSB5.9, QSB6.7, ISC, QSC8.3, ISL and QSL9 Engines, CM850 Electronic Control System, Bulletin 4021416 or Troubleshooting and Repair Manual, Electronic Control System, ISC, QSC8.3 and ISL Engines, Bulletin 3666271.


Air intake or exhaust leaks

Inspect the air intake and exhaust systems for air leaks. Refer to Procedure 010-024.


Air intake system restriction is above specification

Check the air intake system for restriction. Clean or replace the air filter and inlet piping as necessary. Refer to Procedure 010-031.


Charge air cooler is restricted or leaking

Inspect the charge air cooler for air restrictions or leaks. Refer to Procedure 010-027.


Intake manifold pressure sensor is malfunctioning

Check the intake manifold pressure sensor. Refer to Procedure 019-159 in the Troubleshooting and Repair Manual, ISB, QSB4.5, QSB5.9, QSB6.7, ISC, QSC8.3, ISL and QSL9 Engines, Bulletin 4021416 or Procedure 019-061 in Troubleshooting and Repair Manual, ISC, QSC8.3, and ISL Electronic Control System, Bulletin 3666271.


Air compressor connection is loose or damaged

Check the connection between the manifold and the air compressor. Repair or replace if necessary.


Exhaust system restriction is not within specification

Check the exhaust system for restrictions. Refer to Procedure 011-009.


Turbocharger wastegate is damaged or is stuck open

Check the wastegate for freedom of movement. Inspect the wastegate for damage. Refer to Procedure 010-050.


Turbocharger is not correct

Check the turbocharger part number and compare it to the Control Parts List (CPL), Bulletin 3379133 or 4021327. Replace the turbocharger if necessary. Refer to Procedure 010-033.


Turbocharger is worn or damaged

Check the turbocharger for damage. Measure the turbine and compressor wheel clearances. Refer to Procedure 010-033.


Engine power output is low

Refer to the Engine Performance Troubleshooting symptom tree in Section TT.


Excessive load for engine horsepower rating

Reduce vehicle load or use low gear if the engine is industrial. If engine is marine, change propeller(s).

Last Modified:  29-Jul-2005